Electrical resistance unit



Feb. 10, 1925. I 1,526,139

| o. GRONDAHL ELECTRICAL RESISTANCE UNIT Filed Dec. 4, 1922 INVENTOR 7BYQJZ: z

IY ATTORNEY Patented Feb; 10, 1925.

UNITED. STATES PATENT OFFICE.

LABS O. GRONDAHL, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO THE UNIONSWITCH & SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPORATION orPENNSYLVANIA.

ELECTRICAL RESISTANCE: UNIT.

Application filed December 4, 1922. Serial No. 604,673.

To all whom it may concern:

Be it known that I, LARS O. GRoNDAHL, a citizen of the United States,residing at Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented cer-' tain new and useful Improvements inElectrical Resistance Units, of which the following is a specification.

My invention relates to' electrical resistance units, and particularlyto units having the characteristic of varying in resistance in responseto changes in temperature.

I will describe several forms of resistance units embodying myinvention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a view showing in cross-sectionone formof resistance unit embodying my invention. Fig. 2 is a similarview showing a modified form of resistance unit embodying my invention,andFig. 3 is an end view of the unit shown in Fig. 2. Fig. 4: is an endview showing a modification of the unit shown in Figs. 2 and 3. Fig. 5is a view showing one manner of mounting" the units in the precedingviews.

Similar reference characters refer to similar parts in each of theseveral views.

Referring first to Fig. 1, the unit comprises two electricalconductors10 and 11, portions of which are enveloped in a bead T ofthermo-sensitive substance, that is, a substance having thecharacteristic of varying in electrical resistance in response tochanges in temperature. This substance preferably has a'negativetemperature coeflicient and may for example be cupric oxide, cuprousoxide, a mixture of different oxides. or a mixture of one or more oxideswith other substances such as some silicates.

The unit shownin Fig. 1 may be conveniently manufactured by clampin thetwo conductors 10 and 11 in space relation, applying heat to restrictedportions thereof, dipping the heated portions into a powderedthermo-sensitive substance, so that a smallportion of the substanceadheres to the conductors, and repeating the process until av suflicientquantity of the substance has adhered to the conductors to form a bead,

in which they are embedded. As a modification of this process the twoconductors may be clamped in spaced relation and then thermo-sensitive'substance T will increase the temperature of this substance so that itsresistance will decrease, thereby permitting a still greater amount ofcurrent to flow in the circuit. This decrease of resistance will notoccur immediately, however, but, on the other hand, a certain timeinterval will exist between the initial increase of current in thecircuit and the ultimate greater increase of current due to thereduction in the resistance of the therm0-sensitive substance T. Onecharacteristic of the unit, therefore, is that it is slow-acting inoperation.

Referring now to Figs. 2 and 3, one of the conductors, which is heredesignated 10*,

is cylindrical or tube-like in formation, and

is filled with thermo-sensitive substance T. The other conductor 11passes through this substance at substantially the center of the tube 10The unit shown in Figs. 2 and 3 can be constructed in substantially thesame manner as the unit shown in Fig. 1.

Referring to Fig, 4;, the structure herein illustrated is similar tothat shown in Figs. 2 and 3, except that the outer conductor, which ishere designated 10", is trough-like .in formation and is filled with thethermosensitive substance T through which passes the other conductor 11.

Each of the units shown in Figs. 1, 2 and 4, as well as all suitablemodifications thereof, may be mounted in the manner shown in Fig. 5,wherein the reference character 7 designates a glass tube, one endbfwhich is closed and the other end of which is provided with a lamp base8 comprising a shell 12 and a button 9 insulated from the shell. Theconductors 10 and 11 are located within the tube 7 and are connectedrespectively with the shell 12 and the button 9. ,The lamp base 8 isthreaded to fit the ordinary standard lamp socket, thereby facilitatingthe application ofthe resistance unit to an electric circuit. Obviously,the threaded base8 may be replaced by a base of any Resistance unitsembodying my invention may be used in place of slow-acting relays inelectrical apparatus of any kind, but are particularly well suited foruse in connection with railway signaling apparatus.

Although I have herein shown and described only a few forms ofresistance units embodying my invention, it is understood that variouschanges and modifications may be made therein within the scope of theappended claims Without departing from the spirit and scope of myinvention.

' Having thus described my invention, what I claim is: i i

1. A resistance unit comprising a head of a substance the electricalresistance of which decreases with increase in temperature, and twoelectrical conductors in contact with said bead.

2. A resistance unit comprising a bead of copper oxide, and twoelectrical conductors embedded therein.

3. A resistance unit comprising a bead of thermo-sensitive substance,and two conductors embedded therein.

4. A resistance unit comprising a tube like conductor, a bead ofthermo-sensltive 1,52e,1se

substance in said conductor, and a second conductor embedded in saidbead.

5. A resistance unit comprising a troughlike conductor, a bead ofthermo-sensitive substance in said conductor, and a second conductorembedded in said bead.

6. The method of making a thermo-sensitive unit which consists inclamping two electrodes in spaced relation, applying heat to arestricted portion of said electrodes, dipping them into a powderedthermo-sensitive substance so that a small portion of the substanceadheres to the electrodes, heating said adhering substance until it is:said electrodes into molten thermo-sensitive substance to form a beadin which said electrodes are embedded.

In testimony whereof I affix my signature.

LABS o. GRONDAHL.

